December 3, 2012 AT 7:16 pm

Tutorial: Arduino Lesson 4. Eight LEDs and a Shift Register @arduino

In this lesson, you will learn how to use eight large red LEDs with an Arduino without needing to give up 8 output pins!

Although you could wire up eight LEDs each with a resistor to an Arduino pin (like we did for an RGB LED in Lesson 2) you would rapidly start to run out of pins on your Arduino. If you don’t have a lot of stuff connected to your ‘duino its OK to do so – but often times we want buttons, sensors, servos, etc and before you know it you’ve got no pins left. So, instead of doing that, you are going to use a chip called the 74HC595 Parallel to Serial Conveter. This chip has eight outputs (perfect) and three inputs that you use to feed data into it a bit at a time.

This chip makes it a little slower to drive the LEDs (you can only change the LEDs about 500,000 times a second instead of 8,000,000 a second) but its still really really fast, way faster than humans can detect, so its worth it!

In this lesson, you will learn how to use a RGB (Red Green Blue) LED with an Arduino. You will use the analogWrite function of Arduino to control the color of the LED. At first glance, RGB (Red, Green, Blue) LEDs look just like regular LEDs, however, inside the usual LED package, there are actually three LEDs, one red, one green and yes, one blue. By controlling the brightness of each of the individual LEDs you can mix pretty much any color you want.

We mix colors just like you would mix audio with a ‘mixing board’ or paint on a palette – by adjusting the brightness of each of the three LEDs. The hard way to do this would be to use different value resistors (or variable resistors) as we played with in lesson 2. That’s a lot of work! Fortunately for us, the Arduino has an analogWrite function that you can use with pins marked with a ~ to output a variable amount of power to the appropriate LEDs.